Of the semiconductor light emitting elements (hereinafter simply referred to as light emitting element), those comprising an InGaAlP material as the light emitting part emit light of from red to green.
There have been known light emitting elements comprising an n-type GaAs substrate, a light emitting part composed of an InGaAlP material, which is formed thereon, and a current diffusing layer formed on said light emitting part. FIG. 3 schematically shows one embodiment of the structure of such conventional light emitting element. In the example shown in this Figure, a light emitting part 2 formed of an InGaAlP material and a current diffusing layer 3A are sequentially formed on an n-type GaAs substrate 1, and electrodes 4 and 5 are formed in such a way that they sandwich the substrate, the light emitting part and the current diffusing layer in the laminating direction. In this Figure, the current diffusing layer 3A is hatched for emphasis. The light emitting part has a double heterojunction structure wherein an active layer 22 is interposed between an n-type cladding layer 21 and a p-type cladding layer 23, both having a greater band gap. In the following description, an electrode 4 on the substrate side is referred to as a lower electrode and an electrode 5 on the current diffusing layer side as an upper electrode. The current diffusing layer 3A functions to spread the current from the upper electrode to obtain light emission from a wide area of the active layer, and is formed from a material capable of transmitting the light from the light sitting part.
The current diffusing layer aims at spreading the current from the upper electrode toward the wider area of the light emitting part. Accordingly, the resistance of the semiconductor material to be used preferably has a lower resistance. A lower resistance of the semiconductor material can be achieved by setting the carrier concentration higher.
When the carrier concentration of the current diffusing layer is increased by adding a dopant at high concentrations, the dopant spreads to the light emitting part to reach the active layer, and acts as non-radiative recombination centers, which ultimately causes lower luminous efficiency.
In addition, the light emitting element wherein the dopant has spread to the light emitting part has an extremely short service life, thus raising a reliability problem in connection with the current diffusing layer.